Cook the pasta according to the package directions.
Meanwhile, slice beef into thin bite-sized strips against the grain. Mix flour, salt and pepper. Toss beef strips in flour until coated.
Heat 1 tablespoon oil and 1 tablespoon butter in 12” skillet. Brown half the beef and the mushrooms over medium-high heat. Remove and repeat with remaining oil, butter, and beef.
Add onion, garlic and broth to the skillet and cook for 1 minute, scraping up brown bits from the bottom.
Add beef mixture back to skillet. Reduce heat to low. Stir in sour cream and simmer on low until heated through (do not boil).